1. Field of the Invention
The present invention relates to a polygonal mirror apparatus with a polygonal mirror made of a plastic material. More particularly, the present invention relates to a polygonal mirror apparatus with an improved installation structure of a polygonal mirror with respect to a rotor frame.
2. Description of the Related Art
Generally, a polygonal mirror apparatus is used in a laser scanning unit (LSU) employed in devices such as a laser printer, a digital copy machine, a barcode reader, and a facsimile machine, and that scans a beam emitted from a light source of the LSU in a main scan direction using a rotating polygonal mirror.
With the development of technology, a print speed of a device using an LSU has increased. Accordingly, a polygonal mirror apparatus is required to rotate a polygonal mirror at a high speed and to operate for a long period of time. In addition, the polygonal mirror is required to have a reflectance higher than 85% to increase efficiency of a scanning beam. To meet these requirements, a conventional polygonal mirror apparatus uses a polygonal mirror made by performing microprocessing of aluminum with a degree of purity of at least 99%.
Referring to FIG. 1, a conventional polygonal mirror apparatus includes a base 11, and a bearing 13 fixed at the base 11. A rotating shaft 15 is rotatably installed at the bearing 13. A rotor frame 17 is coupled to the rotating shaft 15, a driving source 20, and a polygonal mirror 30.
The driving source 20 is divided and installed at an outer circumference of the bearing 13 and at the rotating shaft 15 to rotate the rotating shaft 15 through electromagnetic power. The driving source 20 includes a stator core 21, a rotor housing 23, and a magnet 25. The stator core 21 is fixed at the outer circumference of the bearing 13 and includes a wound coil 22. The rotor housing 23 is coupled to the rotor frame 17 and surrounds the stator core 22.
The polygonal mirror 30 is rotated by the driving source 20, thereby deflecting and scanning a beam incident into a reflecting mirror 31 provided on a sidewall of the polygonal mirror 30. The polygonal mirror 30 is coupled to an outer circumference of the rotor frame 17 and is fixed thereto with a fixing member 35. The polygonal mirror 30 is made using an aluminum material with a high degree of purity and has a plurality of reflecting mirrors formed through micromachining of metals.
Since the polygonal mirror 30 of the conventional polygonal mirror apparatus having the above-described structure is made using expensive aluminum, the manufacturing cost is high. Moreover, since micromachining of metals is used to form the polygonal mirror 30, productivity is very low. In addition, since the polygonal mirror 30 is fixed to the rotor frame 17 with the fixing member 35, the assembly processes is complicated and the number of parts increases.